This question has to do with the engine. Again, my 1999 F150. It is the V-6 4.2 liter engine and now has about 112K miles on it. I have (for the most part) changed the oil religiously since I bought this truck new. I have never had any mechanical work done to it besides PM. The only problems I am having is the temp knob spins on the shaft now and the odometer doesn't always iluminate right away. Oh, I had an outer tie rod broke a couple years ago but I changed both with no problem.
I have noticed recentley a slight sputter while driving and idling. I took the truck in to a mechanic. He said everything looked fine and suggested a good additive to clean the fuel injectors. I have changed the plugs and wires within the past year. I run a tank of higher octane fuel through it every now and then to clean the engine (in my mind maybe

) and I also run injector cleaner through the tank once in a while. The engine is clean as a whistle and otherwise runs excellent. I am just slightly worried that trouble may be brewing.
Any thoughts on this would be greatley appreciated.